Wireless Power System

ABSTRACT

A higher power wireless power transmitter (HPWPT) including a first, second and third circuit and a transmit coil for wirelessly powering a lower power wireless power receiver (LPWPR) is provided. The first circuit is a switch network. The second circuit is variable impedance network and/or a tuning network. The third circuit is a control logic circuit configured to change the input voltage source or topology of the first circuit, to change the impedance and/or tuning characteristics of the second circuit, to select the transmit coil, vary frequency or duty cycle of the PWM signal or any combination thereof. The change in the input voltage or topology of first circuit or change in impedance or tuning characteristics of second circuit or change in the transmit coil used or the applied constraints on the frequency and duty cycle of the PWM signal constrain the maximum power transmitted by the HPWPT to LPWPR.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional patent application No. 61/672,784 titled “Wireless Power Charging System”, filed in the United States Patent and Trademark Office on Jul. 18, 2012.

The specification of the above referenced patent application is incorporated herein by reference in its entirety.

BACKGROUND

A low power wireless power receiver, for example, rated at 5 Watts (W), when receiving power from a higher power wireless power transmitter, for example, rated at 65 W needs to be protected against excessive power potentially being transmitted from the wireless power transmitter. Conventional wireless power receivers typically have a clamping mechanism to guard against harmful voltage and current conditions which occur when excessive power is received. These clamping mechanisms divert the excess power away from the main circuitry of the wireless power receiver thereby protecting the main circuitry of the wireless power receiver. However, the clamping mechanisms can drain away only up to a certain amount of excess power. This power limit of the clamping mechanism is set at the time of designing the clamping mechanism. When the excess power during the actual operation exceeds this power limit, the clamping mechanism will be damaged and will not be able to protect the main circuitry of the wireless power receiver any further. In that situation, the main circuitry of the wireless power receiver will also suffer permanent damage and the wireless power receiver will become non-functional.

As the lower rated power wireless power receivers could easily be exposed to unsafe power levels while being powered from a higher rated power wireless power transmitter, low power wireless power receivers are very susceptible to damages when used with such wireless power transmitters. Hence, there is a need for a wireless power system that constrains the higher rated power wireless power transmitter to transmit a known level of maximum power which does not exceed the safe limits of the wireless power receiver.

There are several wireless power receivers in the market today such as those built-in into smartphones of LG Nexus4, Nokia Lumia 920/820, HTC Droid, etc., or those in the accessory-sleeves for Apple iPhone, Samsung S3/S4, etc. These wireless power receivers in smartphones and other portables will stop working if placed on top of higher power wireless power transmitters if such techniques as described herein were not implemented.

SUMMARY OF THE INVENTION

The wireless power system and method disclosed herein enables the delivery of a safe amount of power from a higher rated power wireless power transmitter to a lower rated power wireless power receiver. The wireless power system and method disclosed herein constrains the wireless power transmitter to transmit a known level of maximum power through multitude of techniques comprising, for example, an impedance network change, a dynamic topology change, a tuning circuit change, a transmit coil change, transmitter operation in discrete frequency regimes, transmitter operation in discrete duty cycle regimes, transmitter operation at different input voltages etc., and any combination thereof to ensure that a wireless power receiver will not be exposed to unsafe power levels.

A wireless power transmitter for safely charging a wireless power receiver is provided. The wireless power transmitter comprises a first circuit, a second circuit, and a third circuit. The first circuit, for example, a switch network is configured to receive an input voltage. In an embodiment, the first circuit is configured as an inverter in one of multiple inverter topologies, for example, a half bridge inverter topology, a full bridge inverter topology, a class D inverter topology, a class E inverter topology, etc. The second circuit is a variable matching circuit or a tuning circuit or a combination thereof. The second circuit can be used with any first circuit to limit the transmitted power. The second circuit comprises one or more of passive electronic components, active electronic components, and electronic switches for limiting the power transmitted to the wireless power receiver. The second circuit is connected between the first circuit and a transmitter coil. The transmitter coil is configured to wirelessly transmit power to the wireless power receiver.

The third circuit, for example, a control logic circuit is configured to provide a pulse width modulated (PWM) signal to the first circuit. The third circuit is configured to change the input voltage of the first circuit, to drive the first circuit to change a topology of the first circuit, to drive the second circuit to change impedance offered by the second circuit, to drive the second circuit to change its tuning characteristics, to select the transmit coil(s), vary frequency or duty cycle of the PWM signal, etc., or any combination thereof. The change in the input voltage or change in topology of the first circuit or change in impedance offered or tuning characteristics of the second circuit or change in the transmit coil used or the applied constraints on the frequency and duty cycle of the PWM signal limits the maximum power transmitted by the wireless power transmitter to the wireless power receiver.

In an embodiment, the third circuit of the wireless power transmitter determines the maximum power that is to be transmitted to the wireless power receiver based on receiving an implicit message or an explicit message from the wireless power receiver. On receiving and interpreting the message, the third circuit configurably adjusts the maximum power that could be transmitted to the wireless power receiver. The maximum power transmitted to the wireless power receiver is configurably adjusted either by selecting the appropriate input voltage for the first circuit, or by changing the topology of the first circuit, or by changing the impedance offered or by changing the tuning characteristics of the second circuit or by changing the transmit coil used, or by constraining the wireless power transmitter to operate in a frequency regime or a duty cycle regime or by a combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of the invention, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, exemplary constructions of the invention are shown in the drawings. However, the invention is not limited to the specific methods and components disclosed herein.

FIG. 1 exemplarily illustrates a schematic diagram of a wireless power system comprising a higher rated power wireless power transmitter that powers a lower rated power wireless power receiver without exceeding the rated power of the wireless power receiver.

FIG. 2 exemplarily illustrates a first embodiment of the higher rated power wireless power transmitter, where the second circuit is configured as a variable matching circuit to enable safe charging of the wireless power receiver.

FIG. 3 exemplarily illustrates a second embodiment of the higher rated power wireless power transmitter, where the second circuit is configured as a tuning network to enable safe charging of the wireless power receiver.

FIG. 4A exemplarily illustrates a third embodiment of the higher rated power wireless power transmitter, where the second circuit is configured as a tuning network and the first circuit operates as a full bridge inverter.

FIG. 4B exemplarily illustrates a fourth embodiment of the higher rated power wireless power transmitter, where the second circuit is configured as a tuning network and the first circuit operates as a half bridge inverter.

FIG. 4C exemplarily illustrates a fifth embodiment of the higher rated power wireless power transmitter, where the first circuit's inverter topology can be configured as a Class D or Class E depending on the rated power of the wireless power receiver.

FIG. 5 exemplarily illustrates a sixth embodiment of the higher rated power wireless power transmitter, where the maximum power to the wireless power receiver is appropriately constrained by selection of the right wireless power transmit coil.

FIGS. 6A-6C exemplarily illustrate graphical representations showing the power transmitted by the wireless power transmitter to the wireless power receiver as a function of a load applied to the wireless power transmitter.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 exemplarily illustrates a schematic diagram of a wireless power system 100 comprising a higher rated power wireless power transmitter 100 a that provides power to a lower rated power wireless power receiver 100 b, without exceeding the rated power of the wireless power receiver 100 b. In an embodiment, the wireless power system 100 disclosed herein is configured as an inductive wireless power transfer system. The inductive wireless power transfer system comprises a wireless power transmitter 100 a that generates an electromagnetic field to a coupling region for providing energy transfer to the wireless power receiver 100 b. The wireless power transmitter 100 a disclosed herein reconfigures itself to transmit a safe known amount of power sufficient for the wireless power receiver 100 b to deliver its rated power to its load. By constraining its maximum power transmitted, the higher power wireless power transmitter 100 a protects and safeguards the lower power wireless power receiver 100 b. For example, when providing power to a wireless power receiver 100 b rated at 5 W, the wireless power transmitter 100 a rated at 65 Watts (W) reconfigures itself appropriately to provide power within the safe limits. The wireless power transmitter 100 a does not deliver more than that required for the rated power of the wireless power receiver 100 b so as to ensure that the wireless power receiver 100 b will not be damaged.

The wireless power transmitter 100 a disclosed herein comprises a first circuit, a second circuit, and a third circuit. The first circuit is configured as a switch network 102 as exemplarily illustrated in FIG. 1 and FIG. 5. The switch network 102 receives an input voltage and current from an external power source. In an embodiment, the first circuit is configured as an inverter in one of multiple inverter topologies, for example, a half bridge inverter topology, a full bridge inverter topology, a class D inverter topology, a class E inverter topology, etc. The switch network 102 comprises transistors that are configured to change a state, for example, into an on state or an off state, based on signals supplied to the switch network 102 from the third circuit.

The second circuit is configured as a variable matching circuit 103, exemplarily illustrated as a “Zmatch” block in FIGS. 1-2 and FIG. 5, or as a tuning network 301 or 401 as exemplarily illustrated in FIG. 3 and FIGS. 4A-4B. The second circuit 103 comprises one or more of passive electronic components, for example, a resistor, a capacitor, an inductor, a magnetic device, a transducer, etc.; active electronic components, for example, a diode, a transistor such as a metal oxide semiconductor field effect transistor (MOSFET), a bipolar transistor, etc., operational amplifiers, an optoelectronic device, directional coupler, etc., and electronic switches. These electronic components in combination are utilized for limiting the power transmitted to the wireless power receiver 100 b. The second circuit 103 is connected between the switch network 102 and a transmitter coil 107. The transmitter coil 107 is configured to wirelessly transmit power to the wireless power receiver 100 b. The transmitter coil 107 is used for inducing an electromagnetic field to a coupling region for providing energy transfer to the wireless power receiver 100 b. The wireless power transmitter 100 a transmits power to the wireless power receiver 100 b by radiating a required electromagnetic field using the transmitter coil 107. The wireless power receiver 100 b comprises a receiver coil 108 that picks up the electromagnetic field with a certain coupling coefficient that exists between the transmitter coil 107 and the receiver coil 108.

The third circuit is configured as a control logic circuit 104, for example, a state machine, a microcontroller, etc., of the wireless power transmitter 100 a. Analog input signals are converted to digital signals by an analog to digital converter (ADC) 105 operably coupled to the control logic circuit 104 of the wireless power transmitter 100 a. The output signal of the ADC 105 is fed to the control logic circuit 104. The modulator/demodulator block 106 senses, filters and decodes messages from the wireless power receiver 100 b. The output of the modulator/demodulator block 106 is also fed to the control logic circuit 104. The control logic circuit 104 takes inputs from the ADC block 105 and from the modulator/demodulator block 106 and appropriately configures the first circuit, second circuit, transmit coil and input voltage source selection to ensure that a safe amount of power is transmitted to the wireless power receiver 100 b. The control logic circuit 104 also drives the PWM signal to the switch network 102 adhering to the appropriate frequency range and duty cycle range. The control logic circuit 104 enables or disables electronic components in the variable matching circuit 103 using general purpose input/outputs (GPIOs) and switches.

In an embodiment as exemplarily illustrated in FIG. 1, the control logic circuit 104 is configured to change the input voltage source 101 a of the switch network 102. The wireless power transmitter 100 a can receive multiple input voltages sources 101 a, for example, at 5 Volts (V), 12V, 19V, etc., and can switch to different input voltage sources 101 a to transmit a different amount of power to the wireless power receiver 100 b. The change in the input voltage source 101 a limits the maximum power transmitted by the wireless power transmitter 100 a to the wireless power receiver 100 b.

In an embodiment as exemplarily illustrated in FIGS. 4A-4C, the control logic circuit 104 is configured to change the topology of the switch network 102. As exemplarily illustrated in FIG. 4A, the control logic circuit 104 configures the first circuit to operate as a Class D full bridge inverter. As exemplarily illustrated in FIG. 4B, the control logic circuit 104 configures the first circuit to operate as a Class D half bridge inverter. As exemplarily illustrated in FIG. 4C, the control logic circuit 104 configures the first circuit to operate either as a Class D half bridge inverter or Class E inverter. The change in switch network topology limits the maximum power transmitted by the wireless power transmitter 100 a to the wireless power receiver 100 b.

The control logic circuit 104 of the wireless power transmitter 100 a drives the variable matching circuit 103 to change impedance offered by the variable matching circuit 103. The control logic circuit 104 utilizes GPIOs and switches to enable or disable the electronic components in the variable matching circuit 103 and change the impedance of the variable matching circuit 103 accordingly. The change in the impedance of the variable matching circuit 103 ensures that for a given input voltage 101 a, the maximum power transferred is guaranteed to be within a certain limit. The control signal (CTRL) from the control logic circuit 104 limits the amount of power that the wireless power transmitter 100 a can deliver to the wireless power receiver 100 b. For example, a 65 W wireless power transmitter 100 a is programmed to deliver no more than 5 W plus expected losses in the wireless power system 100 to the wireless power receiver 100 b. Specifically, if the expected efficiency of the wireless power system 100 is 70% at 5 W transfer, then the wireless power transmitter 100 a prevents its input power from exceeding 5/0.7=7.14 W. In this case, the wireless power transmitter 100 a configures the variable matching circuit 103 accordingly such that in the range of frequency of operation, maximum input power does not exceed 7.14 W.

As a secondary safety precaution, the wireless power transmitter 100 a disclosed herein monitors input power by monitoring input voltage (Vin) 101 a and input current (Iin) 101 b to ensure that the input power does not exceed beyond the expected power level. This secondary safety precaution accounts for fault conditions such as a short circuit, an open circuit, etc., on the wireless power receiver 100 b side.

In an embodiment, the control logic circuit 104 of the wireless power transmitter 100 a determines the maximum power that is to be transmitted to the wireless power receiver 100 b based on receiving an implicit message or an explicit message from the wireless power receiver 100 b. On receiving and interpreting the message, the control logic circuit 104 adjusts the maximum power that could be transmitted to the wireless power receiver 100 b. The maximum power transmitted to the wireless power receiver 100 b is adjusted either by selecting the appropriate input voltage for the first circuit, or by changing the topology of the first circuit, or by changing the impedance offered or by changing the tuning characteristics of the second circuit or by changing the transmitter coil 107 used, or by constraining the wireless power transmitter 100 a to operate in a frequency regime or a duty cycle regime or by a combination thereof.

FIG. 2 exemplarily illustrates an embodiment of the variable matching circuit 103 configured in the second circuit of the wireless power transmitter 100 a. There are various types of impedance matching circuits such as the L-match networks and Pi-match networks. In this embodiment, an L-match network is used for adjusting the impedance so as to limit the maximum power and enable safe charging of the wireless power receiver 100 b. The switch network 102 may be configured as an inverter in one of multiple inverter topologies and in the embodiment as exemplarily illustrated in FIG. 2, the switch network 102 is configured to operate in a class E inverter configuration. Inductor L1, capacitor C1 and capacitor C2 of the variable matching circuit 103, exemplarily illustrated as a “Zmatch” block in FIG. 2, are configured by the control logic circuit 104 to limit the maximum power transmitted to the wireless power receiver 100 b. Via switches S1 and S2, the capacitor C2 is added to the impedance matching network before L1 or after C1. Switch S1 and S2 are left open if capacitor C2 is not required. The change in the impedance offered by the variable matching circuit 103 limits the power transmitted by the wireless power transmitter 100 a to the wireless power receiver 100 b.

FIG. 3 exemplarily illustrates an embodiment of the tuning circuit configured in the second circuit 103 of the wireless power transmitter 100 a. The switch network 102 may be configured as an inverter in one of multiple inverter topologies and in this embodiment as exemplarily illustrated in FIG. 3, the switch network 102 is configured to operate in a class E inverter configuration. In this embodiment, the resonance operation of the circuit with respect to the operating frequency of the inverter is adjusted via switches S1 and S2 to limit the maximum power and enable safe charging of the wireless power receiver 100 b. For example, in normal operation, the S1 switch and the S2 switch are open and the wireless power transmitter 100 a is capable of delivering 65 W, as exemplarily illustrated in FIG. 6A. In another example, if the S1 switch is closed, then the maximum amount of power can be limited, for example, to 35 W. If the S1 switch and the S2 switch are closed, then the maximum amount of power can be limited, for example, to 5 W. The change in the resonance characteristics of the tuning circuit 103 limits the power transmitted by the wireless power transmitter 100 a to the wireless power receiver 100 b.

The switch network 102 can be operated in a frequency regime. The frequency regime refers to a definite range of frequencies of operation of the switch network 102. In this embodiment, the control logic circuit 104 is configured to restrict the frequency of the PWM signal to the chosen frequency regime. The maximum power delivered by the wireless power transmitter 100 a to the wireless power receiver 100 b is limited to various levels by operating the switch network 102 in different frequency regimes, as disclosed in the detailed description of FIG. 6B.

Furthermore, the switch network 102 can be operated in a duty cycle regime. The duty cycle regime refers to a definite range of duty-cycles of operation of the switch network 102. In this embodiment, the control logic circuit 104 is configured to restrict the duty cycle of the PWM signal to the chosen duty cycle regime. The maximum power delivered by the wireless power transmitter 100 a to the wireless power receiver 100 b can be limited to various levels by operating the switch network 102 in different duty cycle regimes. For a given PWM signal frequency, the PWM signal duty cycle range can be assigned for different power levels, as disclosed in the detailed description of FIG. 6C.

The switch network 400 a in FIG. 4A exemplarily illustrates an embodiment of the switch network 102 of the wireless power transmitter 100 a shown in FIG. 1, where the first circuit is configured as a Class D full bridge inverter 400 a. The switch network 400 b in FIG. 4B exemplarily illustrates another embodiment of the switch network 102 of the wireless power transmitter 100 a shown in FIG. 1, where the first circuit is configured as a Class D half bridge inverter 400 b. For illustration purposes, in FIGS. 4A-4B, the respective switch networks 400 a and 400 b are connected to a tuning circuit and transmit coil L_(TX). FIGS. 4A-4B shows the change in switch circuit topology from a half bridge inverter 400 b to a full bridge inverter 400 a, and vice versa. In this embodiment, the control logic circuit 104 is configured to drive the switch network 102 to change the topology of the switch network 102. The change in the topology of the switch network 102 limits the maximum power transmitted by the wireless power transmitter 100 a to the wireless power receiver 100 b. That is, switching the switch circuit topology from the half bridge inverter 400 b to the full bridge inverter 400 a and vice versa helps limit the maximum power transmitted from the wireless power transmitter 100 a to the wireless power receiver 100 b shown in FIG. 1. For a given fixed input to the wireless power transmitter 100 a, a half bridge inverter 400 b delivers lesser power than the full bridge inverter 400 a. As exemplarily illustrated in FIG. 4A, a full bridge inverter 400 a comprising switches S1, S2, S3, and S4 can be transformed to a half bridge inverter 400 b, as exemplarily illustrated in FIG. 4B, by closing the switch S3 and opening or disconnecting switch S4. In an example, a full bridge inverter 400 a topology can be used to deliver a maximum of 45 W while its reconfigured half bridge inverter 400 b topology may deliver only a maximum of 10 W. This dynamic change in topology is employed to limit the maximum amount of power transmitted wirelessly to the wireless power receiver 100 b.

The switch network 400 c in FIG. 4C exemplarily illustrates another embodiment of the switch network 102 of the wireless power transmitter 100 a shown in FIG. 1. For illustration purposes, in FIG. 4C, the switch network 400 c is connected to a series resonance tuning capacitor and transmit coil L_(TX). The switch network 400 c in FIG. 4C can be configured as a Class D half bridge inverter or Class E inverter. In this embodiment, the control logic circuit 104 in FIG. 1 drives the switch network 102 to change its topology between Class D half bridge inverter and a Class E inverter. The change in the topology of the switch network 102 limits the power transmitted by the wireless power transmitter 100 a to the wireless power receiver 100 b. That is, switching the switch circuit topology from the Class D half bridge inverter 400 c to the Class E inverter 400 a and vice versa helps limit the maximum power transmitted from the wireless power transmitter 100 a to the wireless power receiver 100 b shown in FIG. 1. For a given fixed input to the wireless power transmitter 100 a, a Class D half bridge inverter 400 b delivers lesser power than a Class E inverter 400 a. As exemplarily illustrated in FIG. 4C, the switch network 400 c is transformed into a Class D half bridge inverter by closing switch S1 and opening switch S4. The PWM signal drives switches S2 and S3 to deliver power wirelessly via the transmit coil L_(TX) to the wireless power receiver 100 b. The switch network 400 c is transformed into a Class E inverter by closing switch S2 and S4 and opening switch S1. The PWM signal drives switches S3 to deliver power wirelessly via the transmit coil L_(TX) to the wireless power receiver 100 b. In an example, the switch network 400 c in a Class D half bridge inverter topology may deliver a maximum of 10 W while in a Class E inverter topology may deliver a maximum of 20 W. This dynamic change in topology is employed to limit the maximum amount of power transmitted wirelessly to the wireless power receiver 100 b.

FIG. 5 exemplarily illustrates another embodiment of the wireless power transmitter 100 a, where the control logic circuit 104 in FIG. 1 configures the transmit coil network 500 to enable safe charging of the wireless power receiver 100 b. The transmit coil network 500 in FIG. 5 is implemented using multiple inductors and switches. For example, the wireless power transmitter 100 a uses inductor L_(TX1) to transmit a maximum of 65 W power to the wireless power receiver 100 b by keeping switch S1 closed and switch S2 open. The wireless power transmitter 100 a uses inductor L_(TX2) to transmit a maximum of 5 W power to the wireless power receiver 100 b by keeping switch S1 open and switch S2 closed. The wireless power transmitter 100 a uses multiple coils and switches for transmitting various levels of maximum power to the wireless power receiver 100 b.

FIGS. 6A-6C exemplarily illustrate graphical representations showing the power transmitted by the wireless power transmitter 100 a to the wireless power receiver 100 b exemplarily illustrated in FIG. 1, as a function of a load applied to the wireless power transmitter 100 a. FIG. 6A exemplarily illustrates a graphical representation showing the power transmitted by the wireless power transmitter 100 a to the wireless power receiver 100 b as a function of a load and tuning characteristics of the tuning circuitry illustrated in FIG. 3. If switch S1 and switch S2 are open in FIG. 3, then the maximum amount of power delivered by the wireless power transmitter 100 a to the wireless power receiver 100 b is 65 W. If switch S1 is closed and switch S2 is open, then the maximum amount of power delivered by the wireless power transmitter 100 a to the wireless power receiver 100 b is limited to 35 W. If S1 switch and the S2 switch are closed, then the maximum amount of power delivered by the wireless power transmitter 100 a to the wireless power receiver 100 b is limited to 5 W.

FIG. 6B exemplarily illustrates a graphical representation showing the power transmitted by the wireless power transmitter 100 a to the wireless power receiver 100 b as a function of a load in a frequency regime. For example, the wireless power transmitter 100 a uses a frequency range of f1-f2 Hertz (Hz) to deliver a maximum power of 65 W to the wireless power receiver 100 b. Similarly, the wireless power transmitter 100 a uses a frequency range of f3-f4 Hz to deliver a maximum power of 35 W to the wireless power receiver 100 b. Furthermore, the wireless power transmitter 100 a uses a frequency range of f5-f6 Hz to deliver a maximum power of 5 W to the wireless power receiver 100 b. In an embodiment, the maximum power transmitted to the wireless power receiver 100 b is configurably adjusted by constraining the wireless power transmitter 100 a to operate in a particular frequency regime by varying the frequency of the pulse width modulated signal. For example, the wireless power transmitter 100 a is programmed to operate, for example, at 65 W, 35 W, 5 W, etc., by constraining the wireless power transmitter 100 a to operate in frequency regimes f1-f2 Hz, f3-f4 Hz, f5-f6 Hz, etc., respectively.

FIG. 6C exemplarily illustrates a graphical representation showing the power transmitted by the wireless power transmitter 100 a to the wireless power receiver 100 b as a function of a load in a duty cycle regime. For example, the wireless power transmitter 100 a uses a d1-d2 duty cycle range to transmit a maximum power of 65 W to the wireless power receiver 100 b, a d3-d4 duty cycle range to transmit a maximum power of up to 35 W to the wireless power receiver 100 b, and a d5-d6 duty cycle range to transmit a maximum power of up to 5 W to the wireless power receiver 100 b. Duty cycle regimes can be broken into as many ranges as necessary. In an embodiment, the maximum power transmitted to the wireless power receiver 100 b is configurably adjusted by constraining the wireless power transmitter 100 a to operate in a particular duty cycle regime by varying the duty cycle of the pulse width modulated signal. For example, the wireless power transmitter 100 a is programmed to operate at a maximum power, for example, of 65 W, 35 W, 5 W, etc., by constraining the wireless power transmitter 100 a to operate in duty cycle regimes d1-d2, d3-d4, d5-d6, etc., respectively.

Although the detailed description refers to the switch network 102 being operated in a class E inverter configuration as exemplarily illustrated in FIG. 2, FIG. 3, and FIG. 4C and a class D inverter configuration as exemplarily illustrated in FIG. 4A-4C, the scope of the wireless power transmitter 100 a disclosed herein is not limited to the switch network 102 being operated in a class E inverter configuration or the class D inverter configuration and is extended to be operated in other functionally equivalent inverter topologies. The maximum power transmitted to the wireless power receiver 100 b exemplarily illustrated in FIGS. 1-3 and FIG. 5 is thereby configurably adjusted either by selecting the appropriate input voltage 101 a for the first circuit 102, or by changing the topology of the first circuit 102, or by changing the impedance offered or by changing the tuning characteristics of the second circuit 103 or by changing the transmit coil 107 used, or by constraining the wireless power transmitter 100 a to operate in a frequency range or a duty cycle range or by any combination thereof.

The wireless power system 100 and method disclosed herein enables the delivery of a safe amount of power from a higher rated power wireless power transmitter 100 a to a lower rated power wireless power receiver 100 b. For example, when a smartphone with an integrated wireless power receiver 100 b whose rated power is 5 W is placed on a wireless power transmitter 100 a that includes techniques described herein, the wireless power transmitter 100 a would constrain itself, for example, configure its switch network 102 as a Class D half bridge inverter, configure its tuning network and operate in a frequency range of f5-f6 Hz and duty cycle range of d5-d6% so as to limit the maximum power transmitted. If a tablet with an after-market accessorized wireless power receiver 100 b whose rated power is 15 W is placed on such a wireless power transmitter 100 a, the wireless power transmitter 100 a may switch into a Class E inverter topology, operate at fixed frequency and duty cycle and adjust its Zmatch network so as to not exceed the power limit. If a notebook with a wireless power receiver 100 b whose rated power is 65 W is placed on such a wireless power transmitter 100 a, the wireless power transmitter 100 a may switch into a Class D full bridge inverter topology, increase the input supply voltage, use a different transmit coil and operate in a frequency range of f1-f2 Hz and duty cycle range of d1-d2% so as to increase and yet limit the maximum power transmitted. If a blue-tooth headset with a wireless power receiver 100 b whose rated power is 300 mW is placed on such a wireless power transmitter 100 a, the wireless power transmitter 100 a may configure its switch network 102 as a Class D half bridge inverter, operate at a fixed frequency which is the resonance frequency of the wireless power receiver 100 b, adjust its tuning network and constrain its duty cycle to safe range so as to not exceed the maximum power that the wireless power transmitter 100 a can safely receive.

The foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention disclosed herein. While the invention has been described with reference to various embodiments, it is understood that the words, which have been used herein, are words of description and illustration, rather than words of limitation. Further, although the invention has been described herein with reference to particular means, materials, and embodiments, the invention is not intended to be limited to the particulars disclosed herein; rather, the invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. Those skilled in the art, having the benefit of the teachings of this specification, may affect numerous modifications thereto and changes may be made without departing from the scope and spirit of the invention in its aspects. 

We claim:
 1. A wireless power transmitter for powering a wireless power receiver, said wireless power transmitter comprising: a first circuit configured to receive an input voltage; a second circuit connected between said first circuit and a transmitter coil, said transmitter coil configured to wirelessly transmit power to said wireless power receiver; and a third circuit configured to provide a pulse width modulated signal to said first circuit, wherein said third circuit is configured to perform one or more of: changing said input voltage to said first circuit; driving of said first circuit to change a topology of said first circuit; driving of said second circuit to change tuning characteristics and/or impedance offered of said second circuit; changing said transmitter coil that is used to deliver power wirelessly to said wireless power receiver; and constraining frequency and duty cycle of said pulse width modulated signal to a range of values and varying said frequency and said duty cycle of said pulse width modulated signal within those respective ranges; whereby said change in one of said input voltage, said topology of said first circuit, said tuning characteristics and/or impedance offered of said second circuit, said transmitter coil, said frequency range of said pulse width modulated signal, and said duty cycle range of said pulse width modulated signal limits said power transmitted by said wireless power transmitter to said wireless power receiver.
 2. The wireless power transmitter of claim 1, wherein said first circuit is a switch network.
 3. The wireless power transmitter of claim 1, wherein said second circuit is one of a variable matching circuit and/or a tuning network.
 4. The wireless power transmitter of claim 1, wherein said second circuit comprises one or more of passive electronic components, active electronic components, and electronic switches for limiting said power transmitted to said wireless power receiver.
 5. The wireless power transmitter of claim 1, wherein said third circuit is a control logic circuit.
 6. The wireless power transmitter of claim 1, wherein said first circuit is configured as an inverter in one of a plurality of inverter topologies.
 7. The wireless power transmitter of claim 1, wherein said third circuit is configured to drive said first circuit to change a topology of said first circuit from a Class D full bridge inverter to a Class D half bridge inverter and vice versa.
 8. The wireless power transmitter of claim 1, wherein said third circuit is configured to drive said first circuit to change a topology of said first circuit from a Class D inverter to a Class E inverter and vice versa.
 9. A method for powering a wireless power receiver using a wireless power transmitter, comprising: providing said wireless power transmitter comprising: a first circuit configured to receive an input voltage; a second circuit connected between said first circuit and a transmitter coil, said transmitter coil configured to wirelessly transmit power to said wireless power receiver; and a third circuit configured to provide a pulse width modulated signal to said first circuit; configuring said third circuit of said wireless power transmitter to perform one or more of: changing said input voltage to said first circuit; driving of said first circuit to change a topology of said first circuit; driving of said second circuit to change tuning characteristics and/or impedance offered of said second circuit; changing said transmitter coil that is used to deliver power wirelessly to said wireless power receiver; and constraining frequency and duty cycle of said pulse width modulated signal to a range of values and varying said frequency and said duty cycle of said pulse width modulated signal within those respective ranges; whereby said change in one of said input voltage, said topology of said first circuit, said tuning characteristics and/or impedance offered of said second circuit, said transmitter coil, said frequency range of said pulse width modulated signal, and said duty cycle range of said pulse width modulated signal limits said power transmitted by said wireless power transmitter to said wireless power receiver.
 10. The method of claim 9, further comprising determining maximum power that is to be transmitted to said wireless power receiver by said third circuit of said wireless power transmitter, on receiving one of an implicit message and an explicit message from said wireless power receiver.
 11. The method of claim 10, further comprising configurably adjusting said maximum power transmitted to said wireless power receiver, by said third circuit configuring said first circuit and/or said second circuit in said wireless power transmitter, based on said determination.
 12. The method of claim 9, further comprising configurably adjusting said maximum power transmitted to said wireless power receiver by selecting an appropriate said input voltage for said first circuit, or by changing said topology of said first circuit, or by changing said impedance offered or by changing said tuning characteristics of said second circuit or by changing said transmit coil used to deliver power to said wireless power receiver, or by constraining said wireless power transmitter to operate in a frequency regime or a duty cycle regime or by a combination thereof. 